Excavation machines, for example, hydraulic power shovels are largely constituted by a base carrier and an upper rotary body which is rotatably mounted on the base carrier through a swivel mechanism. Provided on the upper rotary body are an operator's cab to be occupied by a machine operator, and a front working mechanism including a boom, an arm and a bucket. The boom, arm and bucket are driven from hydraulic cylinders, and, for driving these hydraulic cylinders and other hydraulic actuators such as vehicle drive motor and rotating motor, an engine is accommodated on a machine chamber of the vehicle along with hydraulic pump, change-over valve etc.
In order to prevent the front working mechanism from hitting against surrounding buildings or other structures as it is turned in different directions during a ground working operation in a limited space, it is necessary to minimize the radius of turns of the upper rotary body as small as possible. In this connection, there have been developed the so-called ultra-mini turn type hydraulic power shovels which are arranged to have a turn radius within the breadth of the upper rotary body. Disclosed in Japanese Laid-Open Patent Specification H7-243223 is a typical ultra-mini turn type hydraulic power shovel. This prior art ultra-mini turn type hydraulic power shovel is arranged in the manner as will be described below with reference to FIGS. 9 through 13.
Referring first to FIG. 9, indicated at 1 is a base carrier of the machine, and at 2 is an upper rotary body. The base carrier 2 is constituted by a crawler type carrier having a pair of crawler belts 3 along the opposite lateral sides thereof. The upper rotary body 2 is rotatably supported on the base carrier 1 through a swivel base 4. Mounted on top of a frame 5 of the upper rotary body 2 is an operator's cab 6 which is equipped with a driver's seat for an machine operator, along with operating levers and other manual operating or control means. The front working mechanism 7 is largely constituted by a boom 8, an arm 9 and a bucket 10, and provided on the part of the upper rotary body 2. In this instance, as shown in FIG. 10, the operator's cab 6 and the front working mechanism 7 are located side by side in left and right front sections of the upper rotary body 2. Further, denoted at 11 is a machine chamber to accommodate therein hydraulic cylinders which serves as drive means for the front working mechanism, along with an engine, a hydraulic pump, change-over valves and an operating fluid tank for supplying pressure oil to hydraulic actuators such as hydraulic motors or other drive means for vehicle driving and rotating mechanisms of the machine. The machine chamber 11 extend from the rear side of the operator's cab 6 toward a mount base of the front working mechanism 7.
In this case, instead of being directly connected to the upper rotary body 2, the front working mechanism 7 is mounted on a swing post 12 which is connected to the frame 5 of the upper rotary body 2. This swing post 12 is provided for swinging motions of the front working mechanism 7, that is to say, for turning the front working mechanism 7 in the horizontal direction. In this regard, FIG. 11 shows arrangements of a boom foot portion where a base end portion of the boom 8 is connected to the swing post 12. The swing post 12 is horizontally swivellably connected to a vertical swing shaft 13 which is provided on the frame 5 of the upper rotary body 2. The swing shaft 13 is divided into upper and lower portions for passage therethrough of a hydraulic conduit pipe 14. Although not shown in the drawings, a swing drive hydraulic cylinder is connected between the swing post 12 and the upper rotary body 2 in such a way that the swing post 12 is turned through a predetermined angle in the horizontal direction by actuating the swing drive hydraulic cylinder.
The front working mechanism 7 is constituted by the boom 8, arm 9 and bucket 10, which are driven by boom operating hydraulic cylinder 15, arm operating hydraulic cylinder 16 and bucket operating hydraulic cylinder 17, respectively. Proximal ends of the boom 8 and the boom operating cylinder 15 are pivotally connected by pins 18 and 19 to a bracket 12a which is provided on the swing post 12, respectively. The other end of the boom operating cylinder 15 is pivotally connected to the boom 8 by a pin 20, so that the boom 8 is turned up and down through operation of the boom operating cylinder 15. In turn, the arm 9 is pivotally connected to the boom 8 by a pin 21, and opposite ends of the arm operating cylinder 16 are pivotally connected to the boom 8 and arm 9 by pins 22 and 23, respectively. Accordingly, the arm 9 can be turned up and down relative to the boom 8 through operation of the arm operating cylinder 16. Further, the bucket 10 is pivotally supported at the fore end of the arm 9 through a pin 24, while opposite ends of the bucket operating cylinder 17 are pivotally connected to the arm 9 and bucket 10 by pins 25 and 26, respectively. Accordingly, the bucket 10 can be turned up and down by operation of the bucket operating cylinder 17.
In this instance, the boom 8 is divided into upper and lower parts, namely, into a lower boom 8L which is pivotally connected to the swing post 12 by the pin 18 and an upper boom 8U which is pivotally connected to the arm 9 by the pin 21. Further, the lower boom 8 has its fore end portion pivotally connected to a base end portion of the upper boom 8U by a pin 27. The pin 20 which pivotally connects the boom operating cylinder 15 is provided on the part of the lower boom 8L. Accordingly, the term "boom foot portion" refers to a foot portion of the lower boom 8L which is pivotally connected to the swing post 12 by the pin 18.
Denoted at 28 are a pair of cross-links which function to control the open angle between the lower and upper booms 8L and 8U. The cross-links 28 are each constituted by a pipe- or rod-like member, and extended along the opposite lateral sides of the boom 8. Proximal ends of these cross-links 28 are pivotally supported by a pin 29 on and between a pair of brackets 12a which are erected on the swing post 12. The other ends of the cross-links 28 are pivotally connected to base end portions of the upper boom 8U by a pin 30, more particularly, to lateral sides of a base end portion where the upper boom 8U is connected to the lower boom 8L. As seen particularly in FIG. 12, in a maximum lifted position of the boom 8, the center axis of the cross-link 28, that is to say, a line X1 which connects the pins 29 and 30 of the cross-link 28 is intersected by a line X2 which connects pins 18 and 27 of the lower boom 8L.
With the arrangements as described above, when the boom 8 is lifted up and down, the lower boom 8L is vertically turned about the pin 18 which pivotally connects the lower boom 8L to the swing post 12. At this time, the cross-links 28 are turned up and down in interlinked relation with the movements of the boom 8, about the pin 29 instead of the pin 18. Namely, the pin 27 which pivotally connects the lower and upper booms 8L and 8U and the pin 30 at the other ends of the cross-links 28 are turned along arcuate loci of movement T1 and T2, respectively, which have the respective centers at distantly separate points. In addition, the length of the line X1 between the pins 18 and 27 (the radius of the arcuate locus T1) differs from that of the line X2 between the pins 29 and 30. It follows that the arcuate loci T1 and T2 are different from each other in center position and radius.
As shown in FIG. 12, the pin 29 is located in a position which is closer to the pivoting point and slightly lower than that of the pin 18, so that the line X2 has a greater length than the line X1. As a consequence, within the range of up and down movements of the boom 8, the loci T1 and T2 of the pins 27 and 30 intersect with each other twice as the boom 8 is moved from an uppermost lifted position down to a lowermost position. On the other hand, the fore end of the boom 8, namely, the pin 21 which pivotally connects the upper boom 8U and arm 9 draws a locus T3 of a non-circular curve.
As seen in FIG. 9, the boom 8 can be lifted up into the uppermost position to assume a rotating posture as indicated by solid line, or lifted down into the lowermost position to assume a deep-excavating posture as indicated by one-dot chain line or to assume a maximum outreaching posture as indicated by two-dot chain line. In ground excavating operations, normally the boom 8 comes into contact with the ground surface when put in or when in the vicinity of the maximum outreaching posture. In the deep-excavating posture, the depth-wise position of the bucket 10 determines the possible excavation range. In excavating operations, the front working mechanism 7 is largely stretched out in the forward direction when put in or in the vicinity of the maximum outreaching posture, minimizing the open angle between the lower and upper booms 8L and 8U of the boom 8, that is to say, folding and bending the boom 8 as a whole to a greater degree thereby increasing the angle with the ground surface to secure a greater excavation depth. On the contrary, in the rotating posture, for the purpose of receding the front working mechanism 7 into a compact form as a whole and for minimizing the radius of turns, the boom 8 is put almost in an upright position by increasing the open angle between the lower and upper booms 8L and 8U as much as possible.
This is the reason why the open angle of the lower and upper booms 8L and 8U is varied according to the movements of the boom 8. The cross-links 28 are pivotally connected between the upper arm 8U and the brackets 12a of the swing post 12 in such a way that the point of pivotal connection of the cross-links 28 with the upper boom 8U draws the arcuate locus T2 which is different from the arcuate locus T1 of the point of pivotal connection of the lower boom 8L with the upper boom 8U, thereby varying the open angle between the lower and upper booms 8L and 8U as the boom 8 is lifted up and down. Speaking on the basis of an open angle which is taken by the lower and upper booms 8L and 8U at an intersecting point of the loci T1 and T2, the open angle becomes smaller when the pivoting point on the locus T1 is located outside the arc of the locus T2 and becomes larger when the pivoting point on the locus T2 is located outside the arc of the locus T1.
Therefore, as shown in FIG. 12, when the boom 8 is lifted down, the loci T1 and T2 are intersected with each other at a point immediately before the maximum outreaching position, and, from that point, the pin 27 is positioned outside the locus T2 all the way to minimize the open angle between the lower and upper booms 8L and 8U until the deep-excavating position is reached. On the other hand, as the boom 8 is lifted up from the maximum outreaching position to the rotating position, the position of the pin 30 is displaced to the outside of the locus T1. The center positions and radii of the loci T1 and T2 are determined such that the positions of the pins 27 and 30 are set apart from each other to a maximum degree when the boom 8 takes the maximum outreaching position. By so doing, the boom 8 as a whole can be bent to a greater degree at the time of excavating operations, with a smaller open angle between the lower and upper booms 8L and 8U (e.g., angle a in the maximum outreaching position or angle .beta. in the deep-excavating position) to secure a sufficient excavation depth. On the contrary, when the boom 8 is lifted into the rotating position, the lower and upper booms 8L and 8U are spread to a greater angle .gamma. or into an almost straight position to back off the front working mechanism into a compact form. As a consequence, the front working mechanism is contracted to have a small radius of turns S, which falls within the area of the upper rotary body 2 as indicated in FIG. 9, and can be rotated with fewer possibilities of hitting against building walls or other structures which may exist in the vicinity of the upper rotary body 2, particularly when structures are substantially vertical building walls or the like.
In a hydraulic power shovel of the ultra-mini turn type which is arranged as described above, instead of being directly mounted on the upper rotary body 2, the front working mechanism 7 is mounted on the swing post 12 which is protruded to the outside from the upper rotary body 2, for permitting efficient side ditch excavation. Namely, when the hydraulic power shovel as a whole is put in the posture as shown in FIG. 13, the bucket 10 is located in an offset position which is almost in line with one side of the upper rotary body 2. In this position, for example, the front working mechanism 7 is operated to excavate a side ditch along one side of a road or the like, smoothly by means of the bucket 10, while moving the vehicle in a predetermined direction.
Normally, the hydraulic power shovel is in the position as shown in FIG. 10, and shifted to the side-ditch excavating position by swinging the front working mechanism 7 on the swing post 12 through a predetermined angle relative to the upper rotary body 2 as indicated by arrow P in the same figure and, in this state, turning the upper rotary body 2 as a whole in the opposite direction as indicated by arrow Q.
In the above-described prior art, the cross-links 28 are provided on the opposite sides of the boom 8. Therefore, each cross-link 28 is projected from the lateral side of the boom 8, more specifically, from the lateral side of a lower part of the lower boom 8L in the vicinity of the operator's cab, which is located on the upper rotary body 2 side by side with the front working mechanism 7, and machine operating means such as operating levers and operating pedals which are provided on the front side of the operator's cab although not shown in the drawings. Besides, in case the front working mechanism 7 is mounted on a swing post 12 to permit its swinging motions, the cross-links 28 are shifted to positions immediately in front of the operator's cab when the front working mechanism 7 is put in the side-ditch excavating position as shown in FIG. 13, arousing great oppressive sensations in the operator which is seated in the operator's cab for operation of the machine. Especially, in the case of a small-size hydraulic power shovel like the so-called "mini shovel" having the upper rotary body 2 arranged in a compact shape as a whole, the cross-links which are projected from the opposite lateral sides of the boom 8 can come into the way of the operator who is maneuvering the operation control means, restricting to develop excavation machines with a higher degree of compactness.